Ethylene production and ACC-accumulation in Agrobacterium tumefaciens-induced plant tumours and their impact on tumour and host stem structure and function

Abstract

Ethylene emission from wild-type Agrobacterium tumefaciens (C58)-induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo-acoustic spectrometry. Ethylene production was as high as 700 pmol g FW-1 h-1, namely 140 times greater than emitted by non-tumourized control stems. It was highest in 5-week-old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO-production was discovered. Accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), the substrate of ACC-oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour-adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non-transformed, tumour-surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens-induced tumours.